Substantial advances made in recent years in the electronic field have resulted in a reduction in the physical size and cost of electronic circuits and an increase in their speed of operation and reliability. Using the presently available technology, it is now possible to produce more than 1000 circuits on a substrate a few micrometers square with individual circuits having incorporated in their logic numerous components such as transistors, capacitors, resistors and the like.
These advances have been due to significant improvements in the fabrication processes employed for the manufacture of the microelectronic circuits. One such fabrication process which is widely employed for the manufacture of microelectronic circuits is known as microlithography. Using microlithography, a film of a radiation sensitive polymeric material, commonly known as a resist, is applied on a substrate; a portion of the layer of the polymeric material on the substrate is exposed to high energy radiation such as ultraviolet or other types of radiation, an electron beam, x-ray radiation or the like and the exposed resist is developed with a solvent to remove the solubilized portion. Polymeric materials which on exposure to radiation become more soluble are referred to as positive resists. Polymeric materials which become more insoluble as a result of exposure to radiation are referred to as negative resists. When employing a positive resist the exposure to the radiation is believed to reduce the molecular weight of the exposed portion of the polymeric layer. The exposed portion can then be removed or, as it is commonly referred to, developed with a solvent which preferentially dissolves the exposed lower molecular weight polymer, leaving a patterned protective layer of the original higher molecular weight polymer protecting the unexposed area. The resist remaining on the surface of the substrate is then employed as a protective mask to allow the selective etching or other treatment of the exposed portions of the substrate.
Photolithography is one form of microlithography. The exposure of the resist is made with either visible light or ultraviolet radiation. Photolithography has many inherent advantages over the other types of microlithography. The exposure can generally be conducted using relatively low cost apparatus and at ambient conditions. Typicallythe exposure is made by flood exposing the resist with ultraviolet radiation through a mask. This method is fast and inexpensive and makes photolithography especially suitable for mass production of high volume, low cost electronic circuits. However, using the resist materials heretofore suggested, there is a definite limitation with regard to the degree of resolution which is obtainable.
There is a current and anticipated demand for even higher density circuits which require even higher resolution. One of the more successful methods from a technical standpoint to obtain higher resolutions is to utilize a scanning modulated electron beam to expose a resist. However, electron beam lithography is expensive because of the initial high cost of the electron beam apparatus and the relatively low production rates obtainable. Thus, electron beam lithography is not commercially feasible for low-cost mass-produced circuits. Nevertheless, it would be highly advantageous to have a medium which could be exposed by a photolithographic method and which would have the resolution obtainable by exposure with an electron beam.